Color-kinescopes, etc.



M. w. GREEN COLOR Dec; 25, 1951 KINESCOPES, ETC

Filed April 29, 1950 o INVENTOR Jim] W M1 ATTORNEY Patented Dec. 25,1951 COLOR-KINESCOPES. ETC.

Milton W. Green, Princeton, N. J., assignor to Radio Corporation ofAmerica, a corporation of Delaware Application April 29, 1950, SerialNo. 159,071

7 Claims. 1

This invention relates to cathode-ray tubes and will be described asapplied to a color-kinescope of a kind suitable for use in translatingvideo signals, transmitted by any conventional electroniccolor-television system, into color images of the object or scene beingtelevised.

Stated generally, the principal object of the present invention is toprovide a cathode'-ray tube which shall possess all of the followingad-' vantages; (1) Low beam-velocity and low deflection-current, withresulting economies in the construction and operation of the tube andits associated power supply system. (2) Low-initial cost and (3) uniformwide-angle visibility.

More specifically, the present invention contemplates, and its practiceprovides: 1) A colorkinescope employin accelerating voltages of theorder of, say 500 volts, instead of, say, ten kilovolts (as required insome present-day colorkinescopes). (2) A color-kinescope which, in itsconstruction, presents no complex mechanical alignment problems, such asare encountered in kinescopes of the kind employing a two-dimensionalpunctifcrm mask and target assembly. (3) A color-kinescope wherein thesub-elemental phosphor areas, upon which the color-images appear, arecontained on a substantially plane foundation surface, instead of ondiscrete surfaces disposed at different angles with respect to theobserver (as in the case of kinescope employing a "honey-comb" screen).

Stated generally, the foregoing objects and advantages are achieved, inaccordance with the invention, by the provision of a cathode-ray tubecontaining a three-dimensional grille-like target havingsecondary-electron emissive surfaces upon which signal-modulatedelectron-beams, or beam parts, are respectively directed at lowvelocities, and a two dimensional phosphor screen upon which thesecondary-electrons are selectively directed by electron-optical means.

The invention is described in greater detail in connection with theaccompanying drawing, wherein:

Fig. 1 is a view in perspective of a three-gun kinescope embodying theinvention, the dimensions of the groups of phosphor color-areas on thescreen being enlarged the more clearly to indicate their form andpattern of distribution,

Fig. 2 is a greatly enlarged plan view of a small section of theluminescent screen of the kinescope of Fig. 1, the drawing being markedto indicate the color of the light emitted by each sub-elementalphosphor area,

Fig. 3 is a plan view of a stencil which may be iii employed in layingdown the sub-elemental phosphor areas on the foundation surface of thescreen,

Fig. 4 is a side view in perspective showing a phosphor screen and ahoneycomb target constructed and arranged in accordance with theprinciple of the invention,

Fig. 5 is a view in perspective of a corrugated strip ofsecondary-electron emissive metal employed in fabricating the honeycombtarget of Fig. 4.

Fig. 6 is a view from the gun side of the mask and screen assembly ofFig. 4, showing the angles at which the primary-electrons approach theseveral secondary-electron emissive inner faces of the cells of thehoneycomb mask and Fig. 7 is a side view, partly in perspective, showingthe target and screen assembly of Figs. 4, and 6, the drawing beingmarked with equipotential lines to illustrate the manner in which thesecondary-electrons from the inner faces of the target are selectivelydirected to the different color phosphor-areas on the screen.

The kinescope shown in Fig. 1 comprises an evacuated en /elope having abulbous portion or main chamber I which is provided with a translucentwindow 3 through which a color-screen 5 is visible. The screen 5comprises a foundation surface I which may be the inner face of thewindow and, upon said surface, a multiplicity of groups 9 ofsub-elemental picture areas R, B, G, respectively (Fig. 2). When, as inthe instant case, the kinescope is designed to re-create images in threecolors, each of the picturearea-groups 9 comprises a closed,substantially plane, six-sided polygon made up of the three juxtaposedparallelograms R, B, and G shown in Fig. 2. Alternatively, if thekinescope is to be of the two-color variety, the screen pattern may bemade-up of juxtaposed four-sided plane figures (not shown). Each of thesub-elemental areas is coated with a phosphor material capable ofemitting light of a color (e. g. red R. blue B, green G) individual tothat area. when struck by electrons.

The separate phosphor materials may be laid down on the foundationsurface I of the screen through the apertures ll of a stencil l|3 (Fig.3). The stencil l3 may comprise a silk-screen." if the phosphors are tobe laid down by printing, and may be made of metal if the phosphors areto be deposited by settling them from a liquid suspension, in a settlingtank, not shown. In either event, the same stencil, when re-positionedwith respect to the previously applied phosphor areas. may be used inlaying down the (R), green (G). and blue (B) light, respectively,

the materials of which said areas are composed, may comprise: chromiumactivated aluminum berylliate or zinc cadmium sulfide activated withsilver, for the red area's; alpha-willemite activated with manganese orzinc cadmium sulfide activated with silver, for the green areas;silveractivated zinc sulfide and zirconium silicate for the blue areas.

Referring to Fig. 4: In back of the screen 5, and slightly spaced fromit, is a three-dimensional target or grille l5 consisting of many smallhexagonal cells liar. The apertures of each cell correspond in area andin outline with the polygonal groups Sof phosphor areas on thefoundation surface of the screen and are aligned with individual ones ofsaid groups. The axial dimension of the grille I5 is about the same as adiameter drawn between opposite inner faces of one of its hexagonalcells. The grille I! may be fabricated by stacking a large number ofthin metal strips I53 which have previously been formed (as with acorrugating roller, not shown) into the shape shown in Fig. 5.

At least the six inner faces a-a', b-Ji', -0 of each hexagonal cell I52;are constituted of a material having a secondary-electron toprimaryelectron emissive-ratio equal to or greater than one-to-one. Inthe interests of simplicity the entire grille may be constituted of suchamaterial, e. g. silver magnesium. Alternatively, the grille structure lmay be made of copper or other relatively non-emissive material andcoated on all of its inner surfaces with ceasiated silver or otherrelatively highly emisslve material.

It will be observed upon inspection of Figs. 4, 6 and '7, that there isan auxiliary electrode in the form of a metallic film i'i disposed inthe space between the screen 5 and grille it. In the instant case, thisconductive ll comprises aluminum deposited, in vacuo, by an evaporationprocess, on top of the phosphor coatings 9 of the screen 8. It mayhowever comprise a metal chloride (e. g. zinc or tin) applied in theform of a hot sprayto the glass foundation i beneath the phosphor layersii. In either event this film-like electrode it is of microscopicthinness and is transparent to electrons. As will hereinafter more fullyappear, the electrode i'i serves, when suitably energized, to establishan electron-lens field, indicated by the equipotential lines l9 (Fig.'1), in the space between the grille l5 and screen 5. The direct currentpotential required to establish the lens field I9 is applied between theleadsli and 28 (Fig. l), which will be understood to be connected withinthe main chamber 8 to the grille it and screen 5, respectively.

Either a single electron-gun or a battery of three guns may be used withthe target, screen and lens assembly of the present invention. Thekinescope which has been selected for illustration, is of the three-gunvariety. The guns are contained in separate necks 2b, 2'? and 29 (Fig.

l) disposed 120 apart about the longitudinal axis of the envelope. Thevacuous space in said necks and in the bulbous portion i of the envelopeis continuous. when the electron=beams 25b, 21b and 3% (Figs. aresubjected to a scanning movement. pd by the magnetic R, G, B of each,

4 yokes 2511, 21a and My. the beams approach the grille l5 at discreteangles. Each beam "sees but two of the six inner faces a-a', b-b or cc'of the cells I51: of the mask 15. Thus, referring to Fig. 6 the angle ofapproach of the beam 25b is such that it strikes only the two top innerapex faces H of the cell (51:. None of the electrons of which said beamis comprised strike the other faces (b-b' or c-c') nor do any of thempass through the cell without being intercepted by the faces H. Theimpact of the primary-electrons upon said inner faces 11-41 of the cellI53: releases secondary-electrons. which, as shown in Fig. '7, arefocused by the lens field onto an appropriate one of the subelementalphosphor areas (R, B or G Fig. 2.) Similarly, when the beams 2112 or 29benter a cell 152: from the directions of the arrows shown in Fig. 4 theywill release secondary-electrons from the inner surfaces bb', 0-0,respectively. The curvature of the lens-field I9 is such that thesecondary-electrons from said adjacent pairs of emissive surfaces arefocused upon selected ones of the sub-elemental phosphor areas R, B andG on the screen 5.

As with other kinds of "directional screenassemblies, thescreen-assembly of the present invention may be used in a cathode-raytube (e. g. a kinescope or storage-tube) of the onegun variety. When thetube contains but a single electron-gun, the beam is deviated androtated to points corresponding to the points of origin of the three-gunbeams, so that it too approaches the grille 15 at angles individual tothe pairs of surfaces (a-a', b-b', cc') which are allotted to thedifferent sub-elemental areas 9 on the screen 5.

It will be noted that in cathode-ray tubes of the present invention theintensity of the light-images developed upon the screen is, primarily, afunction of the secondary-electron to primary-electron emission ratio ofthe inner faces, (a-a', etc.) of the mask or grille I5. Therefore, thebeam-accelerating voltage need only be a small fraction of that requiredin cathode-ray tubes wherein the intensity of the light depends directlyupon the density and velocity of a beam of primary electrons.

Attention is also called to the fact that since the individual aperturesin the grille i5 correspond substantially in outline and dimensions tothe polygonal groups 9 of phosphor areas, and are mounted directly inline with said groups, no complex problems of parallax arise in plottingthe phosphor pattern on the screen, or in aligning the grille aperturestherewith. The construction of the grille is simplified by the fact thatunlike the honeycomb grille structures heretofore used incolor-kinescopes, the inner faces of the grille cells need not becoated, e. g. with different phosphor compounds individual to differentcolor-components.

Furthermore, since the luminescent phosphor areas upon which the imagesappear, are all disposed in a single plane (or curved) surface. (insteadof upon numerous angularly disposed faces, as in a honeycomb screen) theobservation of said images is not limited to persons positioned directlyin front of the tube-window.

Although the invention has been described as embodied in acolor-kinescope it is believed apparent that its utility is not limitedto cathode-ray tubes containing a colored-ph0sphor screen.

et-J,

What is claimed is:

1. An electron-beam tube comprising an evacuated envelope containing; afoundation surface, a multiplicity of sub-elemental phosphor coveredareas disposed in duplicate groups on said surface, an apertured targetelectrode mounted in spaced relation with respect to said foundationsurface, the apertures in said target corresponding in outline to saidgroups of phosphor areas and disposed in register with respective onesof said groups, and the target surfaces that define the boundaries ofsaid apertures comprising a secondary-electron emissive material;electron-gun means for selectively activating said secondary-electronemissive target surfaces, and electrode means for establishing in thespace between said target and said foundation surface an electron-Jensfield for directing secondary-electrons from selected ones of saidtarget surfaces to particular ones of said sub-elemental phosphor areas.

2. A color-kinescope in accordance with claim .1 and wherein saidelectrode means comprises an electron-transparent metallic layerdisposed between said target electrode and said foundation surface.

3. The invention as set forth in claim 2 and wherein saidelectron-transparent metallic layer is supported upon said sub-elementalphosphor areas.

4. The invention as set forth in claim 2 and wherein saidelectron-transparent metallic layer is supported directly upon saidfoundation surface.

5. A color-kinescope comprising an evacuated envelope having atransparent window and containing an electron-sensitive screen disposedin a position to be viewed through said window. said screen comprising:a transparent foundation surface and a multiplicity of sub-elementalphosphor areas disposed in duplicate polygonal groups on said surface,the sub-elemental areas of each group being constituted of phosphormaterials capable of emitting light of a color individual to that area,an apertured target electrode mounted in spaced relation with respect tosaid surface, the apertures in said target corresponding substantiallyin area and in outline to individual ones of said polygonal groups ofphosphor areas, and the target surfaces that define the boundaries ofsaid apertures comprising a secondary-electron emissive material;electron-gun means for selectively activating said secondary-electronemissive target surfaces, and electrode means for establishing in thespace between said target and said foundation surface an electron-lensfield for directing secondaryelectrons from selected ones of said targetsurfaces to particular ones of said sub-elemental colored-phosphorareas.

6. The invention as set forth in claim 5 and wherein said sub-elementalphosphor areas are disposed in hexagonal groups of three, and thephosphor materials of which said three subelemental areas are comprisedare capable of emitting red, blue and green light respectively.

'7. The invention as set forth in claim 6 and wherein thesecondary-electrons that activate said different light-emissive phosphormaterials are derived respectively from two adjacent ones of the sixsecondary-electron emissi've boundary surfaces of the apertures in saidtarget electrode.

MILTON W. GREEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,481,839 Goldsmith Sept. 13,1949 FOREIGN PATENTS Number Country Date 866,065 France Mar. 31, 1941

